Deletion ofv-chiAfrom a Baculovirus Reduces Horizontal Transmission in the Field

Abstract

f Nucleopolyhedroviruses (NPVs) can initiate devastating disease outbreaks in populations of defoliating Lepidoptera, a fact that has been exploited for the purposes of biological control of some pest insects. A key part of the horizontal transmission process of NPVs is the degradation of the larval integument by virus-coded proteins called chitinases, such as V-CHIA produced by the v-chiA genes. We used recombinant and naturally occurring strains of the Lymantria dispar NPV (LdMNPV) to test horizontal transmission in the field, release of virus from dead larvae under laboratory conditions, and cell lysis and virus release in cell culture. In the field, strains of LdMNPV lacking functional v-chiA genes showed reduced horizontal transmission compared to wild-type or repaired strains. These findings were mirrored by a marked reduction in released virus in laboratory tests and cell culture when the same strains were used to infect larvae or cells. Thus, this study tests the pivotal role of liquefaction and the v-chiA gene in field transmission for the first time and uses complementary laboratory data to provide a likely explanation for our findings.

Genome sequence of Erinnyis ello granulovirus (ErelGV), a natural cassava hornworm pesticide and the first sequenced sphingid-infecting betabaculovirus

“…ErelGV lacks cathepsin and chitinase genes, despite of their importance for promoting baculovirus horizontal transmission [ 48 ]. This feature can explain the integrity of caterpillar flesh and light color after death (Figure 1 A).…”

Field Efficacy and Transmission of Fast- and Slow-Killing Nucleopolyhedroviruses that Are Infectious to Adoxophyes honmai (Lepidoptera: Tortricidae)

“…According to a study of AaIT expressed by recombinant Autographa californica multiple NPV (AcMNPV), the transmission rate of the fast-killing recombinant virus is lower than that of the wild type AcMNPV, because the yield of recombinant virus was lower than that of wild type and because recombinant-infected larvae fell onto the soil before death [ 18 , 29 ]. Liquefaction of infected cadavers is known to enhance horizontal transmission of NPVs and the v-cath and chi genes, encoding cathepsin and chitinase , respectively, are involved in this process [ 30 , 31 , 32 ]. However, the AdhoNPV and AdorNPV genomes do not possess a chi gene, and infected cadavers do not liquefy, in contrast to other NPVs including AcMNPV [ 11 , 13 ].…”

Behavioural manipulation of insect hosts by Baculoviridae as a process of niche construction

“…For example, recombinant strains with egt and chitinase/cathepsin deletions have been created (separately) for LdMNPV, and the effects of the deletion on host behaviour / transmission studied (e.g. egt: [13], and chitinase: [43]). The next step is to disrupt the niche-constructed pathway in an experimental setting.…”

“…The next step is to disrupt the niche-constructed pathway in an experimental setting. One possible experimental design would be to create the four genotypes in our model ( zg,Zg,zG,ZG ) and compare their effects on transmission in the lab and in the field, using the methodology of D’Amico et al [43] (confinement of larval treatment conditions to mesh bags in a naturalistic setting) to measure transmission. Replicating the fitness orderings from our model would provide support to our predictions.…”